Definitions & References

This page outlines the basic principles driving climate change.  Source data and additional information can be found on the U.S. Environmental Protection Agency website.

What are greenhouse gas emissions?

Gases that trap heat in the atmosphere are called greenhouse gases.  Different gases have different thermal absorption, so different gases are typically compared in terms of CO2 equivalents.

  • Carbon dioxide (CO2) enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and other biological materials, and also as a result of certain chemical reactions (e.g., manufacture of cement). It is removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle.
  • Methane (CH4) is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices and by the anoxic decay of organic material in municipal solid waste landfills, swamps, and bogs.
  • Nitrous oxide (N2O) is emitted during agricultural and industrial activities, combustion of fossil fuels and solid waste, as well as during treatment of wastewater.
  • Fluorinated gases: Hydrofluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, powerful greenhouse gases that are emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chlorofluorocarbons, hydrochlorofluorocarbons, and halons). These gases are typically emitted in smaller quantities, but because they are potent greenhouse gases, they are sometimes referred to as High Global Warming Potential gases (“High GWP gases”).

What is the difference between zero carbon and zero GHG emissions?

Carbon Dioxide is one of the greenhouse gases, and is the largest portion of greenhouse gas emissions in the U.S.  In 2017, carbon contributed 82% of all U.S. greenhouse gas emissions, when adjusted to CO2 equivalents. We promote solutions that reduce all greenhouse gas emissions across all industries with particular focus on ensuring the electric power industry reaches zero carbon by 2040.
Source: U.S. Environmental Protection Agency

Why is increased CO2 in the atmosphere an issue?

For more than 800,000 years, atmospheric CO2 levels have increased and decreased cyclically.  In that time, CO2 concentrations peaked at around 300 parts per million (ppm), then would decline before rising again.  These ‘cycles of glaciation’ occurred naturally, and human civilization has flourished during this most recent interglacial period.

Instead of a decline in CO2 levels as anticipated based on historical trends, CO2 concentrations continue to rise and now exceed 400 ppm.  Abundant data quantitatively link this increase to the expansion of agriculture and increasing fossil fuel use.

The last time today’s atmospheric CO2 levels occurred naturally was approximately 3 million years ago. At that time, the north and south poles were ice free, and Canal Street in Richmond, VA was under forty feet of water.

Geologic history suggests that the current levels of CO2 may well lead to sea levels last seen 3 million years ago and to increasingly devastating storms and droughts. The impacts on our weather and wellbeing are evident today; the time to act is now.

Additional information and analysis on the significance of this trend is discussed in “How the World Passed a Carbon Threshold and Why It Matters” by Nicola Jones, published January 2017.

Where can I learn more about the impacts of climate change?

The Intergovernmental Panel on Climate Change recently published a special report “highlights the urgency of prioritizing timely, ambitious and coordinated action to address unprecedented and enduring changes” due to climate change.